The great thing about it is that you have the option of keeping it plugged in with an AC adapter or bring it around with you sans adapter as it is able to run on 4 AAA batteries. It also comes with a USB connector that lets you connect a commercially available USB cable into it and charge your device, especially if your device is able to be charged via USB such as the iPhone/iPod/iPad but we’re going to go out on a limb here and say that you should probably plug the speakers in with the AC adapter should you wish to charge your phone via this method.
It will retail in Japan for about 8,000 Yen which is about $99.